In a gas turbine engine fuel system it is required to limit fuel flow in response to excursion of one or more engine operating conditions outside acceptable limiting values. Such flow limitation may be effected by spilling fuel from the inlet of a main metering valve of the system. Where a spill valve is provided for this purpose it will usually be operated only in response to the aforesaid unacceptable limiting values, and such operation may occur only rarely. In the present invention the flow-limiting spill valve is additionally operated in normal use to ensure that fuel at the main metering valve inlet is at a low pressure when the engine is shut down and has a limited rise in pressure when the engine is started.